As System On a Chip (SOC) products continue to become more highly integrated, the importance of tests becomes more emphasized. In particular, as applications of the SOC products become more varied, products must be warranted to operate properly even in extreme environments. To ensure this, the products are subject to high-temperature tests, low-temperature tests, high voltage stress (HVS) tests, and the like. Temperature tests are indispensable for applications of the SOC products. In particular, a very low temperature test, which is performed at a temperature of approximately −45 to −90° C., is the most difficult for products to pass. While a few leakage failures are demonstrated in high-temperature tests, leakage failures in low-temperature tests are quite common. This is because, at low temperatures, the supercooled atmosphere under a board (also referred to as a “test circuit board, interconnection board, or performance board”) is condensed into a solid state, i.e. “frost”, which may cause a leakage failure. Most test apparatuses for semiconductor packages include structures in which the exterior air continues to flow into a test head (under the board) in order to cool the test head. In this case, a terminal of a socket connected to a semiconductor package is composed of metals and therefore transmits heat at a faster rate than the board. Thus, the frost is generated first at a bottom of the board, especially, in the region of the socket containing solder. Also, while the exterior air flowing past the test head continues to flow past the bottom of the board, the amount of frost increases, which can cause a shorting effect and leakage failure.
Such leakage failures increase the time required for testing characteristics of products. Even worse, the test itself may not be conducted. In particular, since the leakage failures commonly arise at the time of the start of the test at −90° C., there is no precedent for testing of characteristics of products at −90° C.
The leakage failures arise as follows. According to the Clausius-Clapeyron Equation that describes the correlation between saturated vapor pressure (es) and temperature (T), when an atmosphere of a constant humidity falls down below the dew point without change in pressure, the water vapor in the atmosphere becomes supersaturated. At this time, frost or water drops are generated at a bottom of a test board of low temperature, and this leads to the leakage failures during the testing of products. While testing semiconductor products, the leakage failures may cause serious errors in measurements of all items including a function test and an analog test. Accordingly, sources of the leakage current should be removed to complete a very low temperature test.
In conventional attempts to resolve this issue, a material for substituting the atmosphere having the humidity, i.e., a heated dry gas is used to prevent dew condensation or the like at a low temperature (Japanese Publication Patent No. 12-35459, hereinafter referred to as “Reference 1”). In an alternative approach, an insulating liquid or an insulating solid is coated on a board where dew condensation is expected (Japanese Publication Patent No. 6-118136, hereinafter referred to as “Reference 2”).
However, in Reference 1, where a heated dry gas is utilized, because each semiconductor test apparatus of different structure requires an airtight space, a dry gas, a drying passage, a heating board, or a socket guide, the cost of each apparatus model is increased. In addition, since they occupy a large amount of space, considerable costs and space are required for multiple test apparatuses. In addition, since a ventilating device is required for the dry gas, there are many restrictions for its practical use.
Meanwhile, in Reference 2, adhesion of an insulating liquid or insulating solid with a board is of primary importance. In the case of the insulating liquid, when the liquid of very low temperature (−90° C.) is condensed into a solid, the insulator changes in volume. In the case of the insulating solid, due to a difference in thermal expansion between the board and the insulator, dew condensation may be generated in a gap therebetween. As a result, boards and electronic parts attached to the bottoms of the boards may be damaged. Further, in this approach, coating of the insulating liquid or insulating solid on each board is inconvenient, and since the insulating liquid or solid coating cannot be reused, the process involves continuous costs. In addition, after attaching the insulator to the underside of the boards, it is not easy to remove the attached insulator. This makes it difficult to exchange or test the electronic parts.